1. Field Of The Invention:
The present invention relates to a capacitor for capacitive measuring devices with mutually displaceable capacitor elements for the purpose of varying the capacitance of the measuring device as a function of the relative position of the capacitor elements to one another, in which a first capacitor element (2) has patterned electrode areas consisting of individual electrode areas (1) which are applied to a substrate (6) and are electrically connected to one another in a predetermined manner by means of conducting strips (3), where the conducting strips (3) and the electrode areas (1) are located on the same side of the substrate (6) and where between the conducting strips (3) and the electrode areas (1) there is an insulating layer (4) which is interrupted at predetermined contact points (5) such that at these points an electrode area (1a) is electrically connected to a conducting strip (3a) and that a second capacitor element consists of a carrier (12) on which the counter-electrode or counter-electrodes (10) are mounted.
2. Description Of The Prior Art:
Capacitive measuring devices as used e.g. in linear transducers or rotary encoders which operate as electromechanical components to convert mechanical motion into electrical signals by using a variable capacitor are known. In practice, two types of such devices are distinguished, namely linear devices for measuring a linear distance or a linear displacement between an initial and a terminal position on the one hand and, on the other, rotary devices for measuring rotation or the angle between an initial and an angular position achieved after rotary motion. Although the two types of device serve different purposes, the technology described below and the present invention are completely applicable to both types. They also apply equally to all reciprocal configurations of electrodes, electrostatic screens, reflectors and dielectrics known to persons skilled in the art. In every case, the capacitor element experiences a defined change in capacitance per unit of motion, which is transmitted to an electronic measuring system to evaluate the distance travelled by the mechanical measuring element or the angle through which it has travelled. The resolution or graduation of the measurable differences in distance or angle of such capacitive measuring devices depends essentially on the fineness of the individual electrode surfaces, since the more densely these surfaces can be configured adjacent to one another at essentially right angles to the direction of motion of the mechanical measuring element, i.e. the smaller their extent perpendicular to the direction of motion, the smaller the distance to be travelled by the movable part (the counter-electrodes, screen, reflector or dielectric) of the capacitor, in order to produce a clearly defined capacitance change.
In view of the fact that the individual electrode areas have to be linked to one other, on the one hand, and with the electronic display and logic systems, on the other, each electrode area is provided with at least one contact point. Because of the configuration and geometry of the electrode areas, the contact between the individual patterned electrode areas is made from the rear of the capacitor by means of bores or apertures provided through the capacitor electrodes and the substrate bearing said elements, through which the electrode areas are contacted. The size of these bores or apertures not only affects the capacitance of each electrode area, in so far as they are in the active capacitor range, but also essentially defines the minimum dimensions of the electrode areas, since there are geometrical limits to these which must be observed, as a consequence of the mechanical processing. This means, however, that very tight limits apply to the resolution of the mechanical motion with reasonable electrical interpolation, since a relatively large mechanical movement is required to change the capacitance of the capacitive measuring device. It is evident that this will present disadvantages especially in precision measuring technology. There is a further disadvantage of conventional capacitor elements with patterned electrode areas, in that electrically conductive zones must be provided on both sides of a substrate; on the one side the electrode areas of the variable capacitor and on the other side the conducting strips and contact points.
In recent applications of capacitive measuring devices, capacitors with patterned electrode areas have been used in which the electrode areas located adjacent to one another in a bar pattern continue laterally in fine conducting strips, which are then covered with an insulating layer with a number of apertures, through which conducting strips disposed on the insulating layer and at right angles to the electrodes are electrically connected. One of the disadvantages of this embodiment of devices with such capacitor elements, as known in the art, is that it requires a large surface area relative to the effective electrode areas and is thus not well suited for miniaturisation.